1. Field of the Invention
The present invention relates generally to an apparatus and a method for reselecting a Public Land Mobile Network (PLMN) in a mobile communication terminal, and in particular, to an apparatus and a method for reselecting a PLMN when a Subscriber Identify Module (SIM) is in an invalid state since a mobile communication terminal receives a location registration update rejection message. In the invalid state, the mobile communication terminal that received the location registration update rejection message does not receive normal services but receives only emergency services (e.g., Nos. 911 and 411).
2. Description of the Related Art
Generally in an asynchronous mobile communication system (e.g., Global System for Mobile communications (GSM) or Wideband Code Division Multiple Access (WCDMA)), a mobile communication terminal first selects a Public Land Mobile Network (PLMN) to perform location registration in an accessible cell in a target PLMN when the mobile communication terminal is turned on.
FIG. 1 is a ladder type diagram illustrating conventional processes of updating location registration.
Referring to FIG. 1, a mobile communication terminal 100 transmits a location registration update request message 106 to a target PLMN 102 when it is necessary to request the updating of a location registration. The target PLMN is requested to transmit the location registration update request message 106 in accordance with priority among a plurality of PLMNs.
It is necessary to request the mobile communication terminal 100 to update location registration in the following cases.
(1) When a Home PLMN (HPLMN) or a Registered PLMN (RPLMN) is tried to be camped on after the mobile communication terminal is turned on,
(2) When the HPLMN is looked for and is tried to be camp on in a state where the currently camped on cell is not the HPLMN,
(3) When a PLMN having higher priority is tried to be camped on,
(4) When a dual mode User Equipment (dual mode UE) moves from a Radio Access Technology (RAT) having lower priority to a RAT having higher priority.
The target PLMN 102 receives the location registration update request message 106 and, when it is determined that the location registration update request message 106 is a normal request message, transmits a location registration update authorization message 108 to the mobile communication terminal 100. The mobile communication terminal 100 that received the location registration update authorization message 108 selects an accessible cell in the target PLMN 102 to be in an idle state 110.
The target PLMN 102 receives the location registration update request message 106 and, when it is determined that there is a problem in the location registration update request message 106, transmits the location registration update rejection message 112 to the mobile communication terminal 100.
The target PLMN transmits the location registration update rejection message 112 to the mobile communication terminal 100 in the following cases.
(1) LAU (LocAtion Update or Location Area Update) Reject Cause #2: IMSI (International Mobile Station Identity) Unknown in Home Location Register (HLR)
wherein, the case (1) occurs when the mobile communication terminal 100 that is not registered in a HLR having mobile communication terminal information, subscription information, location information, and authorization function transmits the location registration update request message 106.
(2) LAU Reject Cause #3: Illegal Mobile Station (MS)
wherein, the case (2) occurs when the mobile communication terminal 100 using an invalid SIM card transmits the location registration update request message 106.
(3) LAU Reject Cause #6: Illegal ME (Mobile Equipment)
wherein, the case (3) occurs when the stolen mobile communication terminal 100 transmits the location registration update request message 106.
The SIM card of the mobile communication terminal 100 that received the location registration update rejection message 112 is in the invalid state so that only an emergency service can be used.
In the conventional art, when an illegal mobile communication terminal tries to perform a location registration in the network states such as (1), (2), and (3), the illegal mobile communication terminal receives the location registration update rejection message from the target PLMN and does not receive a normal service in the invalid state.
However, when a network state is not like the network states (1), (2), and (3), for example, when roaming can be performed between PLMNs due to a roaming agreement among service operators, the location registration update rejection message can be received due to a network error or a network policy in a process of a normal mobile communication terminal performing roaming from the current PLMN to another PLMN.
According to the above description, when the location registration update rejection message is received, the mobile communication terminal cannot receive a normal service in the invalid state. In order to receive the normal service, a user must turn off and then turn on the mobile communication terminal to perform a process of again selecting a PLMN and to perform the location registration.
Therefore, a method of reselecting a PLMN, in which the current PLMN is tried to be camped on again without turning off and then turning on in the invalid state of the normal mobile communication terminal so that the normal service can be used, and an apparatus therefor are required.